Organic Free Blank

sol 105 view:


with a link to a sol 107 RAC 3D view.

Does the interest in the OFB now indicate that there is a "positive" result that must be checked against a known carbon free sample?

I would think that negative organic results would not need checking.

Here is a report titled "Science Priorities Related to the Organic Contamination of Martian Landers".

All the pdf papers that I googled on the Phoenix organic free blank which were once on the lpl site are no longer available.


sol 109 animation of the sampling of the OFB:

a href="" title="SS109ESF905885624_1C9B6R2L2sqt-3 by hortonheardawho, on Flickr">

Don't know why the image post failed:

Let's try again...


THinking aloud! If the TEGA got one or more positive Organic results but there was scepticism about those results it would make sense to double check using the OFB.

If the OFB blank medium and the sprinkling of Mars dust could be tested separately for organics then the OFB blank medium should test negative.

If organics are in the soil sample the sample on the OFB should give a positive Organic reading.

If Organics are NOT in the soil sample on the OFB there should be a negative reading for organics.

If the OFB blank gives a positive reading for organics It probably means that there was contamination of the blank since leaving earth and that contamination should be statistically likely to have come from Mars.

Thus if the sprinkled soil and the OFB both give positive organic results then it is most likely that Organics have been indeed been detected in the Martian soil.

If there are negative results for both the soil and the OFM blank then it is possible that there are no organics on the surface of Mars but it does not rule out the possibility that the PHoenix instruments are incapable of detecting organics if they are there.

have you seen anywhere where there is an OCB (Organic Containing Blank) blank on the Phoenix? Such a blank would be necessary to ensure that the instruments can indeed detect organics on the surface.


It will take them many months post Phoenix shutting down to investigate all the results from the TEGA. It would not be terribly smart to fail to take a sample from the OFB as a control and then, well after there is any possibility of doing so, detect what could be organics in one of the soil samples.

This samopling is nothing more than good applied common sense.

With respect to your orgainic containing blank - I thought the idea of sterilisation was to preclude the contamination of the area?


I said organics not living creatures.


Good common sense says that if you have eight shots to bag supper, then you don't waste one on target practice -- unless there is already somethin' in the bag.

So the squiggly lines ( thermograms ) can't be read at all until Phoenix is burried up to its, er, solar panels in CO2 show?

The instrument's results seems particularly simple to an old particle physicists eyes: particle count vs. energy.

If I understand the instrument correctly, the mass spectrometer has been "tuned" for isotopes of carbon, nitrogen, oxygen and hydrogen ( 10 parts per billion detection ) so if all thermograms show a peak at, say, 140.25 C then there are only a limited number of molecules containing C, N, O and H that could become gases at that temperature.

So the exact molecule might take some analysis, but the fact that some organic molecule was detected would be immediately apparent.

Here is an intresting paper discussing how the TEGA thermograms can be used to test the super-oxide theory.

Anyway, the OFB is sampled.

The stated policy in this article is that OFB would only be used if organic C is detected by TEGA. However, given the change in policy regarding filling all the ovens before completing the analysis of each one, maybe the policy regarding OFB has also changed?


"The Phoenix OFB will be used only if organic C is detected on Mars by TEGA. The OFB will then be sampled and analyzed, and results will be compared to the organic signatures released by the Martian sample. After OFB analysis, a TEGA run will be conducted on a second sample of the putative organic-containing material to validate the first analysis. High concentrations of organic molecules and possibly organic fragmentation patterns not in the OFB will also contribute to a credible positive identification of organic molecules indigenous to Mars. The high total carbon content in the OFB FM (1.6 μg C g-1 of sample) may require that the total C content in the Martian materials substantially exceed this number, perhaps as much as 10 μg C g-1 of sample before a positive detection of organic molecules on Mars is credible."

This is nothing new.

Things are set up to go a certain way unless they change it due to unforeseen circumstances that may are not be determined to have happened or might happen in any or all procedures based on known and new science or perception of or results that may have effected previous results current conditions not withstanding.

This of course is subject to change. This would be the verbal equivalent of, “JPEG haze.”


I would guess that use of the OFB involves "wasting" a TEGA cell to analyze a known organic-free sample from Earth. This would explain why they would be reluctant to use it unless there was a positive signal from some Martian sample. Of course, circumstances might overcome that reluctance.

Re reply 6 thanks for the link. It was a very interesting read. I defer to you expertise on the ease of deconvolving the thermogram Hort, so my original idea was incorrect - it was not a results delay factor.

Barsoomer in reply 7 has made a real good point. They are filling all ovens and so having a control would indeed be essential just in case. I also wonder whether the loss of inert carrier gas has had more of an impact than they let on. The contribution of the mass spectrometer will have been diluted - but by how much?